1. Field of the Invention
The present invention relates to a large-area mask and an exposure system having the same. More specifically, the present invention relates to a large-area mask, by which level shifting caused by a gravitational load can be prevented, and an exposure system having the same.
2. Description of the Related Art
In recent years, a flat panel display, such as a liquid crystal display (LCD), has been applied in various fields from PCs to televisions. As is well known, the LCD includes a thin film transistor (TFT) substrate, a color filter substrate, and a liquid crystal layer therebetween. Here, each component located on each substrate, for example, a TFT array, a pixel electrode, and a color filter, has been produced by a known photolithographic method.
Meanwhile, as the size of an LCD increases, the size of a substrate and the size of a mask for patterning each component located on the substrate are also increased. FIG. 1 is a cross-sectional view of a typical exposure system including a large-area mask. A photolithographic process for manufacturing a conventional LCD will be described hereinafter with reference to FIG. 1.
An LCD substrate 10 is located on a support 20 of the exposure system. Here, the substrate 10 may be a glass substrate, and a predetermined layer where a pattern will be formed (not shown) and a photoresist layer (or a layer to be cured by light: not shown) are formed thereon. A mask 30 is located over the substrate 10, and a light source 50 is located over the mask 30. Here, the size of photolithographic mask for TFT-LCD is already reached at the size of 1500 mm×1500 mm. Additionally, it will more increase according to the development of equipment and facilities. As illustrated in FIG. 2, such a mask 30 includes a transparent quartz substrate 32 and a light-blocking pattern 35 arranged to form a predetermined shape on one surface of the substrate 32.
When the conventional mask 30 was located over the substrate 10, because of the very large area of the mask 30, the level of a central portion was shifted by a gravitational load. Thus, a deviated distance between the mask 30 and the substrate 10 degraded the quality of exposure process.
Thus, to prevent the level shifting of the mask 30, a plurality of tensile springs 40 was installed at edges of the mask 30. The tensile spring 40 was installed between the edges of the mask and a sidewall of the exposure system to enable the mask 30 located on the substrate 10 to maintain a tense state.
However, as the tensile spring 40 itself is very expensive, installation of the plurality of tensile springs 40 between the mask and the exposure system caused the very high process cost. As a result, the unit production cost of the LCD was increased.